This invention relates generally to laser communication systems and, more particularly, to techniques for increasing the efficiency of communication by lasers. Semiconductor diode lasers are attractive for communications in space because of their compactness and relatively low power consumption. However, for distances of about 40,000 km or more, an average laser power of at least 300 mW is needed to obtain communication rates in the 1 Gbit/s (gigabit per second) range. Single diode lasers are not yet available at this power level. Even with the use of coherent laser arrays to increase power output, there is still a need for a new approach to increase the bandwidth, versatility and reliability of the communication system. Present technology is limited to communications rates of about 1 Gbit/s. Transmission of multiple communication channels involves the use of electronic multiplexing before the diode laser (or array) is modulated, and this approach has inherent reliability problems. Although it has been recognized that wavelength multiplexing might be employed to address some of these problems, filter technology has limited the number of separate wavelengths that can be mixed. No-one prior to this invention has provided a practical solution to the difficulties that wavelength multiplexing poses.